U.S. patent application number 11/437770 was filed with the patent office on 2006-12-14 for piezo-injector driving apparatus.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Noboru Nagase.
Application Number | 20060279592 11/437770 |
Document ID | / |
Family ID | 37440142 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060279592 |
Kind Code |
A1 |
Nagase; Noboru |
December 14, 2006 |
Piezo-injector driving apparatus
Abstract
A piezo-injector driving apparatus overcomes disadvantages
occurring at the start and the end of charging or discharging of a
piezoelectric element while maintaining high responsiveness. At the
start and the end of charging a piezoelectric element, the absolute
value of a change rate of electrical energy of the piezoelectric
element is set lower than in a period between them. Therefore, the
pattern of electrical energy of the piezoelectric element is in the
shape of the letter S. This prevents an excess of energy supplied
to the piezoelectric element at the start of charging and energy
supplied to the piezoelectric element at the end of charging.
Inventors: |
Nagase; Noboru; (Anjo-city,
JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
448-8661
|
Family ID: |
37440142 |
Appl. No.: |
11/437770 |
Filed: |
May 22, 2006 |
Current U.S.
Class: |
347/10 |
Current CPC
Class: |
F02D 2200/0604 20130101;
F02D 41/2096 20130101; H02N 2/067 20130101; F02D 2200/0602
20130101; F02D 2041/2003 20130101; F02D 2200/501 20130101 |
Class at
Publication: |
347/010 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2005 |
JP |
2005-170319 |
Claims
1. A driving apparatus for a piezo-injector including a
piezoelectric element, the apparatus comprising: a driving circuit
for controlling electrical state amounts of the piezoelectric
element that have a correlation with amounts of expansion and
contraction of the piezoelectric element; a setting circuit that,
in control of at least one of the expansion and contraction of the
piezoelectric element, sets the electrical state amounts to
increase an absolute value of a change rate of the electrical state
amounts after a start of the control, and decrease the absolute
value of a change rate of the electrical state amounts before and
end of the control; and an operation circuit that operates the
state amounts via the driving circuit to match the set state
amounts.
2. The driving apparatus according to claim 1, further comprising:
a detector that detects at least one of an operating state of an
internal combustion engine in which the piezo-injector is mounted,
and an operating state of a vehicle in which the internal
combustion engine is mounted, wherein the setting circuit sets a
profile of the state amounts, based on a detection result of the
sensor.
3. The driving apparatus according to claim 2, wherein the setting
circuit sets the profile by variably setting a pattern of the
absolute values of change rates of the state amounts based on the
detection result.
4. The driving apparatus according to claim 2, wherein the setting
circuit increases or decreases the absolute value of a change rate
of the state amounts at each time based on the detection
result.
5. The driving apparatus according to claim 2, wherein: the
detector detects pressure of fuel supplied to the piezo-injector;
and as the pressure of fuel detected by the detector is higher, the
setting circuit makes the pattern of the absolute values of change
rates of operation voltages larger.
6. The driving apparatus according to claim 1, further comprising:
a monitor circuit that monitors the state amounts, wherein the
operation circuit feedback-controls an actual state amount
monitored by the monitoring circuit so that the actual state amount
matches a state amount set by the setting circuit.
7. The driving apparatus according to claim 1, wherein the state
amounts are electrical energy of the piezoelectric element.
8. The driving apparatus according to claim 1, wherein: the driving
circuit includes a switching device for chopper control; and the
operation circuit repeatedly increases and decreases the amount of
a current flowing in the piezoelectric element by repeatedly
turning on and off the switching device to perform the at least one
of the expansion and contraction of the piezoelectric element.
9. A driving apparatus for a piezo-injector including a
piezoelectric element, the apparatus comprising: a driving circuit
for controlling electrical state amounts of the piezoelectric
element that have a correlation with amounts of expansion and
contraction of the piezoelectric element; a setting circuit that
sets the state amounts to decrease a change rate of electrical
energy of the piezoelectric element at an end of charging the
piezoelectric element; and an operation circuit that operates the
state amounts via the driving circuit to match the set state
amounts.
10. A driving apparatus for a piezo-injector including a
piezoelectric element, the apparatus comprising: a driving circuit
for controlling electrical state amounts of the piezoelectric
element that have a correlation with amounts of expansion and
contraction of the piezoelectric element; a setting circuit that
sets the state amounts to increase the absolute value of a change
rate of the electrical state amounts of the piezoelectric element
after the start of discharging the piezoelectric element; and an
operation circuit that operates the state amounts via the driving
circuit to match the set state amounts.
11. A driving apparatus for a piezo-injector including a
piezoelectric element, the apparatus comprising: a driving circuit
for controlling electrical state amounts of the piezoelectric
element that have a correlation with amounts of expansion and
contraction of the piezoelectric element; a detector that detects
at least one of an operating state of an internal combustion engine
in which the piezoelectric element is mounted and an operating
state of a vehicle in which the internal combustion engine is
mounted; a setting circuit that variably sets a pattern for
changing the absolute values of change rates of the electrical
state amounts in at least one processing of expansion and
contraction of the piezoelectric element within one processing
period, based on a detection result of the detector; and an
operation circuit that operates the state amounts via the driving
circuit so that the electrical state amounts match the pattern set
by the setting circuit.
12. A driving apparatus for a piezo-injector including a
piezoelectric element, the apparatus comprising: a driving circuit
for controlling electrical state amounts of the piezoelectric
element that have a correlation with amounts of expansion and
contraction of the piezoelectric element; a setting circuit that
sets a pattern for changing change rates of electrical energy of
the piezoelectric element in at least one processing of the
expansion and contraction of the piezoelectric element within one
processing period; and an operation circuit that operates the
electrical energy via the driving circuit to match the set
electrical energy.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2005-170319 filed on Jun.
10, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to an apparatus for driving a
piezo-injector including a piezoelectric element as an
actuator.
[0003] A conventional piezo-injector driving apparatus controls the
expansion and contraction of a piezoelectric element by charging or
discharging the piezoelectric element in a multi-switching manner.
The multi-switching manner charges and discharges the piezoelectric
element while repeatedly increasing and decreasing the amount of
current flowing via the piezoelectric element by repeatedly turning
on and off a switching device by chopper control.
[0004] The capacitance of the piezoelectric element changes greatly
with temperatures. Accordingly, even if an electrical state amount
having a correlation with an expansion and contraction amount of
the piezoelectric element such as a voltage applied to the
piezoelectric element does not change, an expansion and contraction
amount of the piezoelectric element may change depending on a
change in the temperature of the piezoelectric element.
[0005] Accordingly, as disclosed in JP-2002-136156A, a driving
apparatus makes an on-time in each on-operation on a switching
device constant, and switches from an off-operation to an
on-operation when a current flowing via the piezoelectric element
becomes zero. By performing such on-and-off operations, energy
supplied to the piezoelectric element can be kept substantially
constant regardless of the temperature of the piezoelectric
element.
[0006] The following problems may occur with the chopper control in
such a mode. Since an energy change is large at the start of
charging or discharging the piezoelectric element, a large noise is
generated when the injector is driven. Moreover, since an energy
change is large at the end of charging the piezoelectric element,
the piezoelectric element vibrates heavily. Since an increase in
the vibration causes an increase in energy loss, a final shift
amount of the piezoelectric element cannot be precisely controlled.
Furthermore, since an energy change is large at the end of
discharging, when the valve of the piezo-injector opens, and then
closes, and the piezoelectric element vibrates heavily, the valve
body in the piezo-injector may seat with an increased sound. If the
piezoelectric element vibrates heavily at the end of discharging,
when regenerative control is performed to restore discharge energy,
the amount of energy that can be restored in the piezoelectric
element may decrease.
[0007] It is possible to set a change in electrical energy of the
piezoelectric element small. In this case, however, it takes longer
to open or close the valve of the piezo-injector. Since one merit
of the piezo-injector is to have higher responsiveness than
injectors employing an electromagnetic solenoid or the like as an
actuator, reducing the absolute value of a change rate of
electrical energy may cause loss of the merit.
[0008] Without being limited to the case where electrical state
amounts of the piezoelectric element are operated in the above
mode, in control of the expansion and contraction of the
piezoelectric element, the above problem generally occurs due to an
increase of a change in electrical state amounts at the start or
the end of charging or discharging.
SUMMARY OF THE INVENTION
[0009] The present invention therefore has an object to provide a
piezo-injector driving apparatus that can suitably overcome
disadvantages occurring at the start and the end of charging or
discharging of a piezoelectric element while maintaining high
responsiveness.
[0010] According to a first aspect, a driving apparatus for a
piezo-injector including a piezoelectric element has a driving
circuit for controlling electrical state amounts of the
piezoelectric element that have a correlation with amounts of
expansion and contraction of the piezoelectric element. The
apparatus also has a setting circuit and an operation circuit. The
setting circuit, in control of at least one of the expansion and
contraction of the piezoelectric element, sets the electrical state
amounts to increase an absolute value of a change rate of the
electrical state amounts after a start of the control, and decrease
the absolute value of a change rate of the electrical state amounts
before and end of the control. The operation circuit operates the
state amounts via the driving circuit to match the set state
amounts.
[0011] According to a second aspect, the setting circuit sets the
state amounts to decrease a change rate of electrical energy of the
piezoelectric element at an end of charging the piezoelectric
element. The operation circuit operates the state amounts via the
driving circuit to match the set state amounts.
[0012] According to a third aspect, the setting circuit that sets
the state amounts to increase the absolute value of a change rate
of the electrical state amounts of the piezoelectric element after
the start of discharging the piezoelectric element. The operation
circuit operates the state amounts via the driving circuit to match
the set state amounts.
[0013] According to a fourth aspect, the setting circuit variably
sets a pattern for changing the absolute values of change rates of
the electrical state amounts in at least one processing of
expansion and contraction of the piezoelectric element within one
processing period, based on an engine condition or a vehicle
condition. The operation circuit operates the state amounts via the
driving circuit so that the electrical state amounts match the
pattern set by the setting circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description made with reference to the drawings. In the
drawings:
[0015] FIG. 1 is a schematic diagram showing an engine system using
a piezo-injector driving apparatus according to a first embodiment
of the present invention;
[0016] FIG. 2 is a sectional view showing a piezo-injector used in
the first embodiment;
[0017] FIG. 3 is a circuit diagram showing the driving apparatus of
the first embodiment;
[0018] FIG. 4 is a time chart showing a feedback control mode of
the first embodiment;
[0019] FIG. 5 is a circuit diagram for explaining that power may be
wastefully consumed in a piezoelectric element;
[0020] FIGS. 6A and 6B are time charts showing operation voltage
patterns and patterns of the absolute values of change rates of
operation voltages in the first embodiment;
[0021] FIGS. 7A and 7B are time charts showing patterns of the
absolute values of change rates of operation voltages in the first
embodiment;
[0022] FIG. 8 is a flowchart showing a setting mode of an operation
voltage pattern in the first embodiment;
[0023] FIG. 9 is a circuit diagram showing a piezo-injector driving
apparatus according to a second embodiment of the present
invention;
[0024] FIGS. 10A and 10B are time charts showing electrical energy
patterns and power patterns in the second embodiment;
[0025] FIGS. 11A and 11B are time charts showing power patterns in
the second embodiment;
[0026] FIG. 12 is a flowchart showing a setting mode of an
operation energy pattern in the second embodiment;
[0027] FIG. 13 is a time chart showing the transition of operation
currents in a variant of the first embodiment;
[0028] FIG. 14 is a time chart showing the transition of operation
currents in a variant of the second embodiment; and
[0029] FIGS. 15A to 15C are time charts showing electrical energy
patterns and voltage patterns in a variant of the embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
First Embodiment
[0030] In a diesel engine system shown in FIG. 1, fuel in a fuel
tank 2 is pumped up by a high-pressure fuel feed pump 4, and fed
under pressure to a common rail 6. The fuel stored under high
pressure in the common rail 6 is fed to a piezo-injector PI
provided at each of cylinders of a four-cylinder diesel engine via
a high-pressure fuel passage 8. Each piezo-injector PI is connected
to a low-pressure fuel passage 9 to return fuel leaking from it to
the fuel tank 2.
[0031] The piezo-injector P1 may be constructed as shown in FIG. 2.
Specifically, a columnar needle storing part 12 is provided in a
body 10 of piezo-injector PI. The needle storing part 12 stores a
nozzle needle 14 movable in its axial direction. When the nozzle
needle 14 is seated in a ring-like needle seat part 16 formed in
the top end of body 10, the needle storing part 12 is separated
from the outside (combustion chamber of the diesel engine). On the
other hand, when the nozzle needle 14 leaves the needle seat part
16, the needle storing part 12 is communicated with the outside.
The high-pressure fuel fed to the high-pressure fuel passage 8 is
fed to the needle storing part 12.
[0032] The back surface side of the nozzle needle 14 (the opposite
side of a side opposing the needle seat part 16) opposes a back
pressure chamber 20. The fuel from the high-pressure fuel passage 8
is supplied to the back pressure chamber 20 via an orifice 22. The
back pressure chamber 20 is provided with a needle spring 24 that
presses the nozzle needle 14 toward the needle seat part 16.
[0033] The back pressure chamber 20 can communicate with the
low-pressure fuel passage 9 via a ball 26. When the ball 26 is
seated in a ring-like valve seat part 30 on the side of its back
surface, the low-pressure fuel passage 9 and the back pressure
chamber 20 are disconnected from each other. When the ball 26
shifts toward the top end of the body 10, the low-pressure fuel
passage 9 is communicated with the back pressure chamber 20.
[0034] The ball 26 is coupled with a small-diameter piston 34 on
the side of the valve seat part 30 via a pressure pin 32. The back
side of the small-diameter piston 34 opposes the end of a
large-diameter piston 36 larger in diameter than the small-diameter
piston 34. A shift transfer chamber 38 is formed by being
partitioned by the small-diameter piston 34, the large-diameter
piston 36 and the inner peripheral surface of the body 10. The
shift transfer chamber 38 is filled with proper fluid such as
fuel.
[0035] On the other hand, the large-diameter piston 36 is coupled
with a piezoelectric element PE at the rear of the body 10. The
piezoelectric element PE is secured to the body 10 at the back of a
side opposing the large-diameter piston 36.
[0036] The piezoelectric element PE includes a laminated member
(piezostack) with multiple piezoelectric elements stacked, which
expands and contracts because of inverse piezoelectric effects to
make the piezoelectric element PE function as an actuator.
Specifically, the piezoelectric element PE is a capacitive load,
which expands when charged, and contracts when discharged. The
piezoelectric element PE according to this embodiment uses a
piezoelectric element of a piezoelectric material such as PZT.
[0037] When the piezoelectric element PE is not fed with current
and is in a contracted state, since force is exerted by the
high-pressure fuel of the high-pressure fuel passage 8, the ball 26
and the small-diameter piston 34 are biased in the rear direction
(upward in FIG. 2) and positioned in the rear of the body 10. In
this case, the back pressure chamber 20 and the low-pressure fuel
passage 9 are disconnected from each other by the ball 26.
Accordingly, the nozzle needle 14 is pressed toward the top end of
the body 10 by fuel pressure (the pressure of fuel in the common
rail 6) in the back pressure chamber 20 and the needle spring 24,
and is seated in the needle seat part 16 (valve close state).
[0038] On the other hand, when the piezoelectric element PE is fed
with a current and consequently expands, the ball 26 moves toward
the top end of the body 10. Thereby, the back pressure chamber 20
is communicated with the low-pressure fuel passage 9. As a result,
the pressure of fuel in the back pressure chamber 20 decreases.
When the force by which the high-pressure fuel in the needle
storing part 12 presses the nozzle needle 14 toward the rear of the
body 10 becomes by a predetermined amount greater than the force by
which the fuel in the back pressure chamber 20 and the needle
spring 24 press the nozzle needle 14 toward the top end of the body
10, the nozzle needle 14 leaves from the needle seat part 16 (valve
open state for fuel injection from the injector PI).
[0039] The engine system shown in FIG. 1 includes sensors for
detecting the operating states of the diesel engine, such as a
pressure sensor 40 for detecting the pressure of fuel in the common
rail 6, a crank angle sensor 42 for detecting the angle of a
crankshaft of the engine, a coolant temperature sensor 44 for
detecting the temperature of coolant, and a battery voltage sensor
46 for detecting the voltage of a battery. The engine system
includes a sensor for detecting the operating states of a vehicle
in which the system is installed, such as a vehicle speed sensor 48
for detecting the travel speeds of the vehicle.
[0040] The detection results of these various sensors are applied
to an electronic control unit 50 provided as a piezo-injector
driving apparatus. According to the detection values, the control
unit 50 operates various actuators of the diesel engine such as the
piezo-injectors PI. The control unit 50 may be constructed as shown
in FIG. 3, and charges and discharges the piezoelectric element PE
provided in the piezo-injectors PI in the following manner.
[0041] The control unit 50 includes a driving circuit 52, a charge
switch operation circuit 80, a discharge switch operation circuit
90, and a microcomputer 100.
[0042] Power supplied from a battery B is supplied via a filter 54
to a DC/DC converter 56, which is a booster or step-up circuit. The
DC/DC converter 56 boosts the voltage of the battery B (e.g., 12V)
to a higher voltage (e.g., 200 to 300V) for charging the
piezoelectric element PE.
[0043] The voltage boosted by the DC/DC converter 56 is applied to
a capacitor 58. The capacitor 58 has its one terminal connected to
the DC/DC converter 56 and another terminal grounded via a
resistor. When the voltage boosted by the DC/DC converter 56 is
applied to the capacitor 58, the capacitor 58 stores the charges to
be supplied to the piezoelectric element PE. It is desirable that
the capacitor 58 has such a capacitance (e.g., several 100 .mu.F)
as to cause little change in its voltage as a result of one
charging operation for the piezoelectric element PE.
[0044] A high-potential terminal of the capacitor 58, that is, the
DC/DC converter 56 side, is connected to a high-potential terminal
of the piezoelectric element PE via a series connection between a
charge switch 60 and a charge/discharge coil 62. A low-potential
terminal of the piezoelectric element PE is grounded.
[0045] One terminal of a discharge switch 64 is connected between
the charge switch 60 and the charge/discharge coil 62. The other
terminal of the discharge switch 64 is grounded.
[0046] A diode 66 is connected in parallel to the discharge switch
64. The diode 66 has the cathode connected between the capacitor 58
and the charge/discharge coil 62 and the anode connected to the
grounding side. The diode 66 forms a chopper circuit for charging
the piezoelectric element PE in conjunction with the capacitor 58,
the charge switch 60, and the charge/discharge coil 62, and
functions as a free wheeling (flywheel) diode.
[0047] On the other hand, a diode 68 is connected in parallel to
the charge switch 60. The diode 68 has the cathode connected to the
capacitor 58 and the anode connected to the discharge switch 64.
The diode 68 forms a chopper circuit for discharging the
piezoelectric element PE in conjunction with the capacitor 58, the
charge/discharge coil 62, and the discharge switch 64, and
functions as a free wheeling diode.
[0048] A voltage detection circuit 70 is connected between the
charge/discharge coil 62 and the high-potential terminal of the
piezoelectric element PE. The voltage detection circuit 70 is used
to detect the potential of the high-potential terminal of the
piezoelectric element PE. Specifically, the voltage detection
circuit 70 includes a serial connection of resistors 72 and 74, and
a capacitor 76 connected in parallel to the resistor 74. A voltage
fluctuation of the piezoelectric element PE is smoothed in the
voltage detection circuit 70, and is outputted as a potential
between the resistors 72 and 74.
[0049] A diode 78 connected between the charge/discharge coil 62
and the voltage detection circuit 70 prevents a voltage of the
piezoelectric element PE from becoming negative.
[0050] The charge switch operation circuit 80 receives a voltage
signal outputted from the voltage detection circuit 70 to a voltage
change speed calculation circuit 81, and converts it to a signal
(voltage signal) corresponding to a voltage change rate. The
converted signal is applied to a negative input terminal of a
comparator 82. A reference voltage outputted by a reference voltage
generating circuit 83 is applied to a positive input terminal of
the comparator 82. The comparator 82, a resistor 84 connected
between its output terminal and positive input terminal, and a
resistor 85 connected between its positive input terminal and the
reference voltage generating circuit 83 form a hysteresis
comparator. Accordingly, the output of the comparator 82 inverts to
a logical low level L when a voltage value of an output signal of
the speed calculation circuit 81 rises from less than "reference
voltage +.DELTA.V (.DELTA.V:predetermined value)" to "reference
voltage +.DELTA.V," and then inverts to a logical high level H when
it drops to "reference voltage -.DELTA.V" or less.
[0051] The output of the comparator 82 is inputted to one terminal
of an AND circuit 86. To another terminal of the AND circuit 86, an
output signal of the one-shot circuit 87 that outputs a signal of
logical high level H for a predetermined period after a driving
signal inputted from the outside becomes a logical high level is
inputted. On the other hand, an output signal of the AND circuit 86
is applied to the charge switch 60 after its power is converted by
the driver 88.
[0052] The discharge switch operation circuit 90 has the same
circuit 91 as the charge switch operation circuit 80. Furthermore,
the discharge switch operation circuit 90 includes an inversion
amplifier 92 that inverts the positive/negative polarity of an
output signal of the voltage detection circuit 70 and outputs the
inverted signal to the same circuit as the speed calculation
circuit 81. Furthermore, the discharge switch operation circuit 90
includes an inverter 93 that captures the driving signal and
outputs the signal logically inverted to the same circuit as the
one-shot circuit 87.
[0053] On the other hand, the microcomputer 100 outputs the driving
signal and a command signal for setting a reference voltage of the
reference voltage generating circuit 83, based on detection values
of various sensors for detecting the operating states of the diesel
engine and the operating states of the vehicle.
[0054] FIG. 4 shows the mode of charging processing and discharging
processing. In FIG. 4, (a) shows the transition of the driving
signal that is outputted from the microcomputer 100 and indicates
an injection period. (b) shows the transition of output of the
one-shot circuit 87. (c) shows the transition of output of a
one-shot circuit in the discharge switch operation circuit 90. (d)
shows the transition of an operation signal of the charge switch
60. (e) shows the transition of an operation signal of the
discharge switch 64. (f) shows a current (operation current) I
flowing via the piezoelectric element PE. (g) shows the transition
of voltages (operation voltages) V of a high-potential terminal of
the piezoelectric element PE. (h) shows the transition of the
absolute values of change rates of the operation voltage V.
[0055] As shown in FIG. 4, when the driving signal outputted from
the microcomputer 100 is applied to the charge switch operation
circuit 80 at time t1, chopper control is started by turning on or
off the charge switch 60 by the charge switch operation circuit 80.
That is, with the driving signal being applied, a signal of logical
high level is outputted for the predetermined period from the
one-shot circuit 87. Since, at this point, the reference voltage
Vref is higher than the voltage value of a signal outputted by the
speed calculation circuit 81, a signal of logical high level is
outputted from the comparator 82. Therefore, the AND circuit 86
produces a logical high level, and the charge switch 60 is turned
on. With the charge switch 60 being turned on, a closed-loop
circuit comprising the capacitor 58, the charge switch 60, the
charge/discharge coil 62, and the piezoelectric element PE is
formed. Thereby, the electric charge of the capacitor 58 is
discharged to charge the piezoelectric element PE. At this time,
the amount of current (operation current) I flowing through the
piezoelectric element PE increases, and the voltage (operation
voltage) V of the high-potential terminal of the piezoelectric
element PE rises.
[0056] However, when the rise speed of the operation voltage V
becomes higher than the reference voltage Vref by the predetermined
value .DELTA.V at time t2, the output of the comparator 82 inverts.
Thus, the output of the AND circuit 86 also inverts to a logical
low level, and the charge switch 60 is turned off. With the charge
switch being turned off, a closed-loop circuit comprising the
charge/discharge coil 62, the piezoelectric element PE, and the
diode 66 is formed. Thereby, the flywheel energy of the
charge/discharge coil 62 is charged to the piezoelectric element
PE. At this time, the operation current decreases. When the rise
speed of the operation voltage becomes lower than the reference
voltage Vref by the predetermined value .DELTA.V at time t3, the
charge switch 60 is turned on again.
[0057] Since, in the above mode, step-down chopper control in which
the charge switch 60 is operated is performed over times t1 to t4
during which the output of the one-shot circuit 87 is at logical
high level, the piezoelectric element PE is charged, and the
potential of the high-potential terminal of the piezoelectric
element PE rises.
[0058] On the other hand, when the driving signal inverts at time
t5, chopper control is started by turning on or off the discharge
switch 64 by the discharge switch operation circuit 90. That is,
with the driving signal being applied, a signal of logical high
level is outputted for the predetermined period from the one-shot
circuit within the circuit 91, whereby chopper control is performed
over the predetermined period. Specifically, with the discharge
switch 64 being turned on, a closed-loop circuit is formed by the
discharge switch 64, the charge/discharge coil 62, and the
piezoelectric element PE. Thereby, the piezoelectric element PE is
discharged. At this time, the amount of current flowing via the
piezoelectric element PE decreases. Furthermore, with the discharge
switch being turned on, then turned off, a closed-loop circuit is
formed by the capacitor 58, the diode 68, the charge/discharge coil
62, and the piezoelectric element PE. Thereby, the flywheel energy
of the charge/discharge coil 62 is restored to the capacitor 58. At
this time, the amount of current flowing via the piezoelectric
element PE increases.
[0059] Since step-up chopper control in which the discharge switch
64 is operated is performed in the above mode, the piezoelectric
element PE is discharged, and the potential of the high-potential
terminal of the piezoelectric element PE decreases. By thus
charging or discharging the piezoelectric element PE, the operation
voltage V of the piezoelectric element PE can be
feedback-controlled. The operation voltage V indicates an
electrical state amount having a correlation with the quantity of
expansion and contraction of the piezoelectric element PE. By
operating the voltage of the piezoelectric element PE, the
expansion and contraction of the piezoelectric element PE can be
controlled. When the absolute value of the change rate of operation
voltages at charge start time and at discharge start time is
excessively large, the noise of the piezo-injector PI may become
large because a great force is conveyed to the body 10 of the
piezo-injector PI when the piezoelectric element PE starts to
move.
[0060] When the absolute value of the change rate of operation
voltages at charge end time is excessively large, the vibration of
the piezoelectric element PE becomes large. When the vibration of
the piezoelectric element PE is large, the amount of energy
consumed wastefully due to factors other than energy for driving
the piezoelectric element PE becomes large. This is because an
equivalent circuit of the piezoelectric element PE is formed, as
shown in FIG. 5, by a mechanical component represented as a series
circuit of LCR and an electrical component represented by a
capacitor connected in parallel to a series circuit of LCR and a
series equivalent resistor connected in series with the parallel
circuit. Therefore, when the piezoelectric element PE vibrates, the
quantity of current consumed by the series equivalent resistor
increases, and the amount of energy consumed wastefully without
making a contribution to the driving of the piezoelectric element
PE increases. An increase in such a loss of energy will reduce
control precision of expansion and contraction of the piezoelectric
element PE.
[0061] Furthermore, when the absolute value of the change rate of
operation voltages at discharge end time is large, the ball 26
shown in FIG. 2 is seated in the valve seat part 30 at an
increasing speed, the sound at the time of the seating may
increase, and the ball 26 may be bounded after being seated in the
valve seat 30, opening the valve of the nozzle needle 14 again.
Additionally, when the absolute value of the change rate of
operation voltages at discharge end time is large, energy loss due
to an increase in the vibration of the piezoelectric element PE may
reduce the amount of energy restored to the capacitor 58.
[0062] In this embodiment, the absolute value of the change rate of
operation voltages is increased after the charging or discharging
of the piezoelectric element PE is started, and the absolute value
of the change rate of operation voltages is decreased when the
charging or discharging is terminated.
[0063] FIGS. 6A and 6B show examples of setting operation voltages
in this embodiment. FIG. 6A shows the transition of operation
voltage during charging, and the transition of the absolute values
of change rates of operation voltages during charging. FIG. 6B
shows the transition of operation voltage during discharging, and
the transition of the absolute values of change rates of operation
voltages during discharging. As shown in FIGS. 6A and 6B, the
profiles of operation voltages shown in solid lines are in the
shape of the letter S during charging, and in the shape of a mirror
image of the letter S during discharging. This can be achieved by
reducing the absolute values of change rates of operation voltages
at start time and at end time, and increasing them in a period
between them. The case in which the above absolute values are
constant is shown by alternate long and two short dashes line.
[0064] FIGS. 7A and 7B show other examples of a mode of setting
operation voltages in this embodiment. FIGS. 7A an 7B both show the
transition of the absolute values of change rates of operation
voltages. In any of these cases, the absolute values of change
rates are set small at start time and at end time, and set large in
a period between them. Specifically, FIG. 7A shows an example that
the absolute values of change rates of operation voltages increase
in stages (two stages in this example) like FIGS. 6A and 6B, and
then decreases in stages (two stages in this example). FIG. 7B
shows an example that the absolute values of change rates of
operation voltages are continuously increased, and then
continuously decreased.
[0065] Changing the absolute values in the period of charging or in
the period of discharging can be performed by changing the
reference voltages in the charge switch operation circuit 80 or the
discharge switch operation circuit 90 as shown in FIG. 3.
[0066] Processing for achieving operations in the modes shown in
FIGS. 6A, 6B and FIGS. 7A and 7B may be made by the microcomputer
100 as shown in FIG. 8.
[0067] In this processing, at step S10, an operation voltage
pattern is selected based on the voltage of the battery B detected
by the battery voltage sensor 46, the vehicle speed detected by the
vehicle speed sensor 48, the rotation speed detected by the crank
angle sensor 42, and the temperature of coolant detected by the
coolant temperature sensor 44. The selection of a pattern of
operation voltages denotes that one is selected from among the
plural patterns illustrated in FIGS. 6A, 6B, 7A, 7B as the patterns
of the absolute values of change rates of operation voltages during
charging.
[0068] An optimum pattern as the above pattern is changeable
depending on the operating states of the engine and the operating
states of the vehicle. For example, during idle rotation control
under a vehicle speed of zero, there is no annoying noise in the
vehicle and a sound generated by the piezo-injector P1 is prone to
be recognized as a noise by a user. Accordingly, it is desirable
that the sound generated by the piezo-injector P1 is controlled.
When the temperature of the piezo-injector PI is low, the friction
between the body 10 and various members (nozzle needle 14,
small-diameter piston 34, and large-diameter piston 36, and the
like) that move in the body 10 becomes large. Therefore, this fact
must be taken into account to decide the above pattern. When the
temperature of fuel fed to the piezo-injector PI is low, the
viscosity of the fuel increases. Therefore, this fact must also be
taken into account to decide the above pattern. Furthermore, if the
voltage of the battery B is low at cold engine starting, since the
piezoelectric element PE cannot be desirably charged, in some
cases, it is desirable to preferentially perform the operation of
increasing the amount of charging for the piezoelectric element
PE.
[0069] From such a viewpoint, a pattern is selected based on the
above parameters. Here, vehicle speed and rotation speed are
examples of parameters for determining whether a given situation is
the situation in which the noise of the piezo-injector PI is easily
recognized by a user, and coolant temperature is an example of a
parameter having a correlation with the temperature of the
piezo-injector PI and the temperature of fuel.
[0070] Step S12 calculates the magnitude of a required operation
voltage, based on the pressure of fuel in the common rail 6
detected by the fuel pressure sensor 40. The fuel pressure is a
factor to change energy required to open the valve of the
piezo-injector PI. This is because, to open the valve of the
piezo-injector PI, that is, to shift the nozzle needle 14 shown in
FIG. 2 toward the rear of the body 10, a force must be generated by
the piezoelectric element PE to overcome a force by which the fuel
in the high-pressure fuel passage 8 pushes the ball 26 to the valve
seat part 30. Therefore, in this embodiment, the magnitude of
operation voltages is set to be changeable according to a fuel
pressure.
[0071] Step S14 sets a final operation voltage pattern from the
pattern selected by the Step S10 and the magnitude calculated by
Step S14. This is done by multiplying the operation voltage pattern
by a correction factor as shown by alternate long and short dash
line in FIGS. 6A and 6B. Specifically, by multiplying the absolute
value of a change rate of operation voltages in each of periods T1
to T3 shown in FIG. 6A by a same correction factor, the absolute
value of a change rate of an operation voltage at each time is
enlarged (or reduced) with an equal magnification. Also, by
multiplying the absolute value of a change rate of operation
voltages in each of periods T4 to T6 shown in FIG. 6B by a same
correction factor, the absolute value of a change rate of an
operation voltage at each time is enlarged (or reduced) with an
equal magnification. Likewise, for the patterns of the absolute
values of change rates of operation voltages shown in FIGS. 7A and
7B, a value at each time is multiplied by a same correction
factor.
[0072] Step S16, to match the final operation voltage pattern,
outputs a command signal for setting a reference voltage outputted
by the reference voltage generating circuit 83 of the charge switch
operation circuit 80 shown in FIG. 3, and the reference voltage of
the discharge switch operation circuit 90. Thereby, feedback
control is performed by the charge switch operation circuit 80 and
the discharge switch operation circuit 90 so that the absolute
value of a change rate of operation voltages of the piezoelectric
element PE made equal to that set at step S14.
[0073] According to the first embodiment, the following advantages
will be provided.
[0074] (1) In charging or discharging of the piezoelectric element
PE, operation voltages are set so that the absolute value of a
change rate of the operation voltages is increased after the
charging or discharging of the piezoelectric element PE is started,
and the absolute value of a change rate of the operation voltages
is decreased when the charging or discharging is terminated.
Thereby, while high responsiveness is maintained, disadvantages
occurring at the start and the end of charging or discharging of
the piezoelectric element PE can be suitably overcome.
[0075] (2) Based on the operating states of a diesel engine and the
operating states of a vehicle in which the engine is mounted, a
profile (pattern of an operation voltage pattern) representing the
transition of operation voltages with respect to time is selected.
Thereby, under the condition of restraining a noise level within a
permissible range, high responsiveness and other requirements can
be suitably satisfied.
[0076] (3) When a fuel pressure in the common rail 6 is higher, a
pattern of the absolute values of change rates of operation
voltages is made greater in magnitude. Thereby, when a required
driving force is greater, a greater driving force can be supplied
to the piezoelectric element PE, so that a driving force most
fitted to a need can be afforded.
[0077] (4) With a correction factor corresponding to the pressure
of fuel in the common rail 6, the absolute value of a change rate
of operation voltages is increased or decreased. Thereby, even if
required energy is different, a profile can be easily set.
[0078] (5) Operation voltages are monitored by the voltage
detection circuit 70 and the like, and feedback control is
performed to make a pattern in which actual operation voltages are
set. Thereby, actual operation voltages can be made to match the
pattern.
[0079] (6) The circuit 52 for driving the piezoelectric element PE
includes switching devices (charge switch 60 and discharge switch
64) for chopper control, by repeatedly turning on and off these
elements, the amount of current flowing through the piezoelectric
element PE is repeatedly increased and decreased to control the
expansion and contraction of the piezoelectric element PE. Thereby,
the piezoelectric element PE can be charged and discharged with a
simple construction.
Second Embodiment
[0080] The capacitance of the piezoelectric element PE tends to
change greatly depending on temperatures. Accordingly, even if the
same operation voltage is applied, the amount of expansion or
contraction (shift amount) of the piezoelectric element PE may
change depending on temperatures. When voltages applied to the
piezoelectric element PE are operated to control the expansion and
contraction of the piezoelectric element PE, the expansion rate and
the contraction rate of the piezoelectric element PE also change
depending on temperatures. Accordingly, control of the expansion
and contraction of the piezoelectric element PE that uses voltages
applied to the piezoelectric element PE as operation amounts
involves difficulties attributed to a change in temperatures of the
piezoelectric element PE.
[0081] In the second embodiment, as an operation amount for
controlling the expansion and contraction of the piezoelectric
element PE, electrical energy flowing into the piezoelectric
element PE from the outside is used. The relationship between the
electrical energy (integral value of voltage and current of the
piezoelectric element PE) and an expansion and contraction amount
of the piezoelectric element PE is not so heavily dependent on a
change in temperatures. Accordingly, by using the electrical energy
as an operation amount, an expansion and contraction amount and an
expansion and contraction rate of the piezoelectric element PE can
be precisely controlled without performing temperature
corrections.
[0082] For this reason, a control unit 50 is constructed as shown
in FIG. 9. Although very similar to the control circuit 50 in the
first embodiment (FIG. 3) in many aspects, the control circuit 50
in FIG. 9 is provided with a voltage detection circuit 110 that
detects a voltage of a high-potential terminal of the piezoelectric
element PE. The voltage detection circuit 110 comprises a series
connection of resistors 112 and 114, and a voltage between the
resistors 112 and 114 is applied to a power monitor circuit 118.
The power monitor circuit 118 monitors power (a change rate of
electrical energy of the piezoelectric element PE) flowing into and
out of the piezoelectric element PE, based on the above voltage,
and a voltage (a voltage value corresponding to a current flowing
through the piezoelectric element PE) between the piezoelectric
element PE and the resistor 116, and generates a power signal (a
voltage value in this example) corresponding to the power to a
charge switch operation circuit 80 and a discharge switch operation
circuit 90.
[0083] The power signal is applied to a negative input terminal of
a comparator 82 in the charge switch operation circuit 80. A
circuit 91a in the discharge switch operation circuit 90 has the
same construction as the charge switch operation circuit 80. A
signal to which the power signal is inverted by the inversion
amplifier 92 is applied to a negative input terminal of a
comparator in the circuit 91a.
[0084] FIGS. 10A and 10B show examples of electrical energy
patterns according to this embodiment. FIG. 10A shows the
transition of electrical energy E during charging, and the solid
line shows the transition of the absolute values of change rates
dE/dt of the electrical energy E during charging. FIG. 10B shows
the transition of electrical energy E during discharging, and the
solid line shows the transition of the absolute values of change
rates dE/dt of the electrical energy during discharging. The
profiles of electrical energy E are in the shape of the letter S
(solid line) during charging, and in the shape of a mirror image of
the letter S (solid line) during discharging. This can be achieved
by reducing the absolute values of change rates of electrical
energy at start time and at end time, and increasing them in a
period between them. The case in which the above absolute values
are constant is shown by alternate long and two short dashes
line.
[0085] FIGS. 11A and 11B show other examples of a mode of setting
electrical energy in this embodiment. FIGS. 11A and 11B both show
the transition of the absolute values of change rates dE/dt of
electrical energy. In any of these cases, the absolute values of
change rates of electrical energy are set small at start time and
at end time, and set large in a period between them. Specifically,
FIG. 11A shows an example that the absolute values of change rates
of electrical energy are increased in stages (two stages in this
example), and then decreased in stages (two stages in this
example). FIG. 11B shows an example that the absolute values of
change rates of electrical energy are continuously increased, and
then continuously decreased.
[0086] Processing for achieving the above operation may be
performed by the microcomputer 100 in the manner shown in FIG.
12.
[0087] In the series of processing, at step S20, an electric energy
pattern is selected based on the voltage of the battery B, a
vehicle speed, a rotation speed, and the temperature of coolant.
The selection of a pattern of electrical energy denotes that one is
selected from among the plural patterns illustrated in FIGS. 10A,
10B, 11A and 11B as the transition of the absolute values of change
rates dE/dt of electrical energy E. The reason of the pattern-based
selection is the same as that at step S10 in FIG. 8.
[0088] Step S22 calculates required energy, based on the pressure
of fuel in the common rail 6 detected by the fuel pressure sensor
40. Step S24 sets a final pattern of electrical energy so that the
pattern selected at Step S20 matches the energy calculated at Step
S22. The setting of the final pattern is performed by increasing or
decreasing the absolute value of a change rate at each time with an
equal magnification, as shown by the alternate long and short dash
line in FIGS. 10A and 10B, like step S14 in FIG. 8.
[0089] Step S26, to match the final pattern of electrical energy,
outputs a command signal for setting a reference voltage outputted
by the reference voltage generating circuit 83 of the charge switch
operation circuit 80 shown in FIG. 9, and a reference voltage of
the discharge switch operation circuit 90. Thereby, feedback
control is performed by the charge switch operation circuit 80 and
the discharge switch operation circuit 90 so that a change rate of
electrical energy of the piezoelectric element PE is equal to that
set at step S24.
[0090] In this second embodiment, as an operation amount for
controlling the expansion and contraction of the piezoelectric
element PE, electrical energy is used. Thereby, a shift amount of
the piezoelectric element PE can be precisely controlled regardless
of a change in temperatures. Specifically, when a final pattern of
electrical energy is equal to a pattern shown by the sold line in
FIG. 10A, a shift amount of the piezoelectric element PE is
determined corresponding to the amount of electrical energy
supplied to the piezoelectric element PE having an area (hatched
portion) enclosed by the solid line, and the shift amount hardly
fluctuates regardless of a change in the temperature of the
piezoelectric element PE.
[0091] According to the second embodiment, in addition to the above
advantages (1) to (6) of the first embodiment, the following
advantages are provided.
[0092] (7) As an operation amount for controlling the expansion and
contraction of the piezoelectric element PE, electrical energy of
the piezoelectric element PE is used. Thereby, even if the
temperature of the piezoelectric element PE fluctuates, the
absolute value of a shift rate of the piezoelectric element PE can
be maintained at an appropriate value.
Other Embodiments
[0093] The above embodiments may be modified as follows.
[0094] In control of the expansion and contraction of the
piezoelectric element PE, as a means for setting state amounts so
that the absolute value of a change rate of electrical state
amounts is increased after the start time, and the absolute value
is decreased at the end time, change rate patterns or patterns do
not need to be symmetrical between a start time and an end time.
The above absolute value may be different between a start time and
an end time. Even if state amounts are set in the above modes only
for expansion control, disadvantages occurring during the expansion
control can be suitably overcome.
[0095] As a method for expanding or reducing the absolute values of
an operation voltage V and electrical energy E at each time based
on the pressure of fuel in the common rail 6, the calculation is
not limited to multiplication by a single correction factor.
Different correction factors may be multiplied among start time,
end time, and a period between them. Furthermore, correction values
may be added instead of multiplying correction factors.
[0096] In the first embodiment, operation voltages are monitored,
and to match the operation voltages to a set pattern, feedback
control is performed by turning on and off the charge switch 60 and
the discharge switch 64. However, the control is not limited to
this embodiment. For example, as shown in FIG. 13, when the amount
of current flowing via the piezoelectric element PE reaches a
predetermined upper limit UL, the charge switch 60 and the
discharge switch 64 are switched from ON to OFF, and when the
amount of current becomes zero, the charge switch 60 and the
discharge switch 64 are switched from OFF to ON. In this case, if
the upper limit ULs of the start time and the upper limit ULe of
the end time of charging or discharging are set lower than an upper
limit ULm in a middle period between them, the patterns shown by
the solid lines in FIGS. 6A and 6B can be obtained. By presetting
the upper limits ULs, ULm, ULe, open control can be performed. As a
means of thus operating the driving circuit 52 to match the set
state amounts, the embodiment is not limited to a means of feeding
back state amounts to be monitored to the set state amounts. The
operation voltage pattern shown in FIG. 7A can be achieved by
setting upper limits in two stages in a period between the start
time and the end time of charging or discharging.
[0097] In the second embodiment, power flowing into and out of the
piezoelectric element PE is monitored, and to match the power to a
set pattern, feedback control is performed by turning on and off
the charge switch 60 and the discharge switch 64. However, the
second embodiment is not limited so. For example, as shown in FIG.
14, an on-operation time is set to a predetermined value, and an
off-operation may be switched to an on-operation when the amount of
current flowing via the piezoelectric element PE becomes zero. In
this case, by setting on-operation times T1 and T3 of the start
time and the end time of charging or discharging smaller than an
on-operation time T2 in a middle period between them, the patterns
shown by the solid lines in FIGS. 10A and 10B can be obtained. The
power pattern shown in FIG. 11A can be achieved by setting an
on-operation time in two stages in a period between the start time
and the end time of charging or discharging.
[0098] For example, when an electrical energy pattern shown in FIG.
15A is used, since a rise rate of electrical energy of the
piezoelectric element PE decreases at the end of charging, the
above problem occurring because of an excess of energy supplied at
the end time of charging the piezoelectric element PE can be
suppressed. Moreover, for example, when an operation voltage
pattern shown in FIG. 15B is used, since a fall rate of operation
voltages of the piezoelectric element PE at the start of
discharging is small, the above problem occurring because of an
excess of the absolute value of a change rate of operation voltages
at the start of discharging the piezoelectric element PE can be
suppressed. Furthermore, when an electrical energy pattern shown in
FIG. 15C is used, since a fall rate of electrical energy of the
piezoelectric element PE at the start of discharging is small, the
above problem occurring because of an excess of a fall rate of
energy at the start of discharging the piezoelectric element PE can
be suppressed.
[0099] An apparatus for driving the piezo-injector PI is not
limited to those shown in FIGS. 3 and 9. A circuit for calculating
power supplied to the piezoelectric element PE is not limited to
the circuit that calculates power, based on a voltage of a
high-potential terminal of the piezoelectric element PE and a
current flowing via the piezoelectric element PE, as shown in FIG.
9. In place of the circuit, the electric power may be calculated
based on the amount of current flowing via the capacitor 58 shown
in FIG. 9 detected by detecting a potential between the capacitor
58 and the resistor 59 (node A). The product of the current amount
and a voltage of the capacitor 58 (specifically, an average value
in the short period) is equal to power supplied to the
piezoelectric element PE. If setting is made so that the voltage of
the capacitor 58 is little affected by charging processing and
discharging processing, power can be simply calculated based on the
above current value.
[0100] A driving circuit may be used which performs chopper control
by using a flyback current of a transformer, as disclosed in JP
8-177678A. The piezoelectric element PE may be charged or
discharged by a method other than chopper control.
[0101] The structure of the piezo-injector PI is not limited to the
structure shown in FIG. 2. Besides injectors that perform two-way
operations such as valve opening and valve closing according to a
shift of a piezoelectric element, injectors are also available
which can continuously adjust a lift amount of a nozzle needle
according to a shift of the piezoelectric element PE, as disclosed
in U.S. Pat. No. 6,520,423. However, when a motive power transfer
system in the piezo-injector PI that transfers the motive power of
the piezoelectric element PE is constructed so that fuel pressure
is applied in opposition to a shift of the piezoelectric element PE
when the piezoelectric element PE starts to shift, it is
particularly effective to variably set patterns of state amounts
and the absolute values of change rates of the state amounts
according to the fuel pressure.
[0102] Internal combustion engines, without being limited to diesel
engines, may be gasoline engines of in-cylinder injection type.
* * * * *